tracefs: fix a leak in eventfs_create_events_dir()

tracefs: fix a leak in eventfs_create_events_dir()

[ Upstream commit 798a401660a151633cb171738a72a8f1efb9b0b4 ]

If we have LOCKDOWN_TRACEFS, the function bails out - *after*
having locked the parent directory and without bothering to
undo that.  Just check it before tracefs_start_creating()...

Fixes: e24709454c45 "tracefs/eventfs: Add missing lockdown checks"
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>